This invention relates to a tape cassette, and more particularly, to a tape cassette having a separate guide for guiding tape along the open front of the tape cassette, opposite the magnetic head of an external tape player/recorder apparatus.
A tape cassette is usually made by joining substantially planar top and bottom halves together to house two tape reels and tape which runs therebetween. A tape cassette also includes a tape guide structure which is either formed integrally of the two halves along an open front wall region thereof or is molded independently and is positioned at the front wall region during assembly. In operation, a magnetic head of an external tape player/recorder apparatus is inserted into the open front wall region to contact the tape running across the tape guide.
To ensure optimum sound reproduction, it is critical that the tape crossing the magnetic head be oriented exactly "perpendicular" to the planes of the cassette halves to ensure proper contact between running tape and the magnetic head. Deviation from exact "perpendicularity" usually is the result of misalignment of the tape at the tape guide.
In order to avoid misalignment of the tape, the tape guide must be designed and manufactured according to strict structural parameters to ensure guiding of the tape in as "perpendicular" an orientation as possible. Of course, such careful design and manufacturing is expensive. On the other hand, because of the vast quantities of compact cassettes made and sold, economy of construction is also important and must be balanced against the strict structural parameters required for an effective tape guide.
Up until now, this balance has been attempted by molding the tape guide entirely of plastic, whether the tape guide is formed integrally of the top and bottom halves of the tape cassette or molded independently thereof.
For example, U.S. Pat. No. 3,934,842, issued to Posso, teaches a tape cassette comprising top and bottom halves of a tape cassette and an independent one-piece tape guide molded entirely of plastic. More particularly, the independent tape guide is made up of an elongated molded body, integral at its back with two longitudinal ribs having a notch therebetween for receiving a pin extending from the bottom half of the cassette which holds the tape guide in the longitudinal direction. There is also formed on the front a plurality of transverse tabs, a left pair of which cooperates with lugs located on the bottom half of the cassette to hold the tape guide in the transverse direction. There is also an aperture formed in the lower half of the cassette which combines with a member extending from the external tape player/recorder to position the tape cassette relative to the tape player/recorder.
Each of the plurality of tabs is designed to require a central notch whose edge is rounded. This series of round-edged notches in the plastic molded tabs is co-planar and defines the tape sliding surface along the open front wall region of the tape cassette.
Finally, the tape guide of the '842 patent comprises a pressing member having a rigid support plate positioned centrally thereof for urging the tape against the magnetic head during operation. To this end, the most centrally located pair of tabs have projections formed integrally thereon in the shape of inclined ramps and adjacent bosses are formed integrally of the body of the tape guide. The rigid support plate of the pressing member is pressed against the ramps such that the plate deforms with its ends being housed between the projections and bosses.
The '842 patent states that the above-discussed tape guide design provides an absolutely perpendicular sliding surface for the tape to travel along. This design, however, actually has several inherent drawbacks which frustrate the realization of the "balance" between optimum "perpendicularity" and cost efficiency.
Firstly, the "perpendicularity" of the tape sliding surface is only as good as the molding process used to form the tape guide, most particularly, the tabs and the notches in the tabs. As suggested in the '842 patent, molding plastics to exacting structural specifications can be very difficult and expensive, and the more exacting the specifications of the molded product, the greater the chance for mold imperfections, especially where cost of manufacturing is a preoccupation.
Secondly, since the independent tape guide is designed to be positioned stationary relative to the cassette, if the area of the tape player/recorder intended for receiving the cassette is not perfectly co-planar relative to the top and bottom of the tape guide, or vice versa, the tabs and notches formed on the tape guide will not be properly oriented relative to the magnetic head. Thus, "perpendicularity" of the tape at the magnetic head would again be negatively effected.
More particularly, as discussed in the later U.S. Pat. No. 4,166,593, issued to Milants (which generally teaches away from the use of an independent tape guide), in a conventional two-part cassette housing having the tape guide molded integrally of each half of the tape cassette, guides project from the bottom cassette half and the top cassette half. When molding either such housing half, it is necessary to provide a taper of "draft" in those parts which extend substantially in the direction in which the mold is opened, so that the housing can be removed easily from the mold. Because of this draft the tape guide molded thereby does not possess true cylindrical surfaces about axes perpendicular to the planes of the cassette halves, but have more of a conical shape. A deterioration of tape playing/recording quality is inevitable with this construction.
In contrast to the conventional construction described above, the tape guide of the '842 patent teaches that the independent tape guide is molded with the mold interface perpendicular to the bottom cassette half wall so that the tape sliding surface can be "theoretically" perpendicular to the support planes. This independent tape guide unit is then fixedly mounted in a corresponding box-shaped recess in the cassette.
However, as emphasized in the '593 patent, the overall accuracy of the tabs and notches comprising the tape sliding surface depends greatly on the cumulative dimensional tolerances of the box-shaped recess and the tape guide in its entirety, and also on the tolerances observed during assembly. Moreover, the top and the bottom of the independent tape guide, like the conventional two-piece cassette described above, each are tapered to provide "draft", so that these surfaces by which the independent tape guide is mounted in the tape cassette may again provide an unwanted oblique relationship between the tape guide and the bottom of the box-shaped recess.
Thirdly, due to the relative rigidity of the pressing member used with the independent tape guide of the '842 patent, it is possible that the pressing member could exert an uneven or non-"perpendicular" pressure upon the tape. In addition, the interference fit between the pressing member and the projections and bosses formed on the tape guide may result in a distortion of the front radius of the tape guide. These factors again could frustrate "perpendicularity".
A fourth and final drawback of the tape guide of the '842 patent is that it requires molding parts on the bottom half of the cassette which are different than parts molded on the top half of the cassette and thus, this design prevents use of identical top and bottom halves which, of course, increases manufacturing costs.
From the foregoing, it can be seen that an improved tape guide for a tape cassette is desired which can be accurately formed, but which is relatively simple in structure such that it may be made easily through automation, and which effectuates optimum orientation of the tape in the tape cassette crossing the magnetic head of a tape player/recorder.